Cathodic Protection Requirements for Deepwater Systems

Field and laboratory experience related to requirements for cathodic protection (CP) in deep water are reviewed with emphasis on identification of the major variables that need to be specified for successful deepwater CP designs for offshore structures. The subject is addressed based on the historical development of cathodic protection design methodologies for offshore structures focusing on sacrificial anode systems and trends that have resulted in specific changes in design requirements. Three main subjects are discussed: (1) application of existing industry standards such as NACE RP0176; (2) environmental factors — dissolved oxygen, temperature, salinity, pH, water velocity and fouling; and (3) calcareous deposits — difference between shallow and deep waters. Current practice of design criteria and systems for deepwater applications is assessed, including initial polarization, use of coatings and anode materials. The results from laboratory tests are compared with available documented service experiences and field tests results.